YOKOTA AIR BASE, Japan — A century before Columbus discovered America, Chinese naval vessels many times bigger than the Santa Maria sailed the high seas, reaching as far as Africa.

But, unlike European voyages of discovery, the Chinese efforts did not forge a global empire. Beset by internal strife, China abandoned its naval efforts, and by 1500, it was a capital offense to build a seagoing junk with more than two masts.

Today, fueled by a booming economy, Chinese naval power is on the rise again.

The People’s Liberation Army (PLA) Navy has been producing frigates, destroyers, submarines and missile boats at an unprecedented rate. In September, it commissioned its first aircraft carrier, the 74,406-ton Liaoning.

U.S. naval commanders, ordered to move the bulk of their fleet to the Pacific theater, say it’s clear that China is building a “blue-water navy,” capable of sustained operations across oceans and able to project power far from the home country.

The U.S. has denied its “Pacific pivot” is directed at China but has called for “transparency” from the PLA.

“They are not making clear why they require these sorts of forces,” said Jan Van Tol, a retired U.S. Navy captain who is a senior fellow at the Center for Strategic and Budgetary Assessments in Washington. He noted that China wouldn’t need an aircraft carrier to seize Taiwan since the island, which China regards as rebellious province, is well within range of mainland air fields.

One reason for a blue-water navy could be for China to protect its trade routes, rather than relying on the U.S. to guarantee freedom of navigation, Van Tol said.

The Chinese government reported imports and exports worth $3.87 trillion in 2012, surpassing, for the first time, those of the U.S. — valued at $3.82 trillion by the U.S. Commerce Department.

China also could be seeking to emulate the U.S. ability to project naval power and build influence, Van Tol added.

“The Chinese now want to do whatever the Americans can do and say: `We are here in the region,’” he said.

Col. Lui Mingfu, of the PLA’s National Defense University, told Australian media in February that China’s goal is to force the U.S. out of the Western Pacific.

Mingfu said American strategic influence would be confined "east of the Pacific midline" as it is displaced by Chinese power throughout East Asia, including Australia.

Such rhetoric is being noted by people like Capt. James Fanell, deputy chief of staff for intelligence and information operations at the U.S. Pacific Fleet. He recently told the U.S. Naval Institute in San Diego that the PLA Navy regularly operates in the Pacific and Indian Oceans and maintains a robust presence around the East and South China seas.

“These moves into the 'distant seas' would seem inevitable for a nation as large as China,” he said. “But it goes without saying that this expansion into blue waters is largely about countering the Pacific Fleet.”

China’s Xinhua news agency reported that a PLA Navy destroyer and two frigates exercising in the Western Pacific earlier this year were practicing maritime confrontation, open-sea mobile combat, law enforcement and open-sea naval commanding.

“Make no mistake, the PLA Navy is focused on war at sea and about sinking an opposing fleet,” Fanell said.

There is evidence that the PLA Navy has ambitions even beyond the Pacific.

Van Tol said China sent a frigate through the Suez Canal in 2011 to evacuate citizens during unrest in Libia, and Chinese ships have participated in anti-piracy efforts off the coast of Somalia.

According to a Dec. 10 Congressional Research Service report on Chinese naval modernization, the PLA Navy comprises 275 vessels: 75 warships, 60 submarines, 55 amphibious ships and 85 small missile boats. The U.S. Navy’s current strength is 285 ships and submarines.

Despite the similarities in numbers, Van Tol said it’s hard to compare the navies. A vessel that the Chinese might describe as a “frigate” might not be deemed worthy of the class in the U.S., he said, but added: “They have certainly been building at a vigorous rate.”

China has a large commercial ship-building industry capable of producing high-quality vessels.

Some of its latest naval designs, such as the Lanzhou-class destroyers, are equipped with powerful radar. Since 2004, the Chinese have launched more than 80 new Houbei-class missile boats, and they are acquiring increasingly advanced diesel submarines, Van Tol said.

Ralph Cossa of the Pacific Forum in Hawaii said China’s submarine fleet is the best that Russia will sell or can be copied. But he added: “The Russians aren’t selling their very best to China.”

China’s anti-submarine warfare capability remains weak, said Lyle Goldstein, an associate professor in the China Maritime Studies Institute at the U.S. Naval War College in Newport, R.I.

The Chinese have mounted a massive research effort to improve their sonar capabilities but will likely lag at least two decades behind the U.S. and its allies, he said.

“Certainly for the next decade there is a major gap to be exploited,” he said. “We need to make the investments today to keep that gap in play.”

U.S. attack submarines have the firepower and survivability to be a strong deterrent and should be spared from budget cuts, he warned.

“I think we could do with fewer carrier battle groups and putting that money towards attack submarines fleet, which is of primary importance,” he said. “That is America’s sharpest weapon.”

The anti-ship ballistic missile (ASBM) that the Chinese are developing would be a powerful weapon although there’s no indication of a successful test against a moving target at sea, he said.

Compared with the Soviet Union’s naval build-up — which involved launching a new submarine every month during the height of the Cold War — the Chinese effort is more deliberate, he said.

“The carrier program has gone forward but it is fairly slow,” he said. “They don’t seem to be in a great hurry. It is within China’s capabilities to build a navy that looks like the U.S. Navy in 15 years, but they may be more restrained.”

The PLA Navy’s lack of combat experience is another question. The U.S. Navy has had 90 years to reach its current level of proficiency in aircraft carrier operations, Van Tol said.

“It took a lot of training and accidents before we got good at it,” he said. “The Chinese are just starting down that road, and it’s hard to predict where they will go.”

“The Chinese are improving, but there is no question that the Japanese navy is far superior in terms of technology, training and sustaining operations,” he said.

The PLA Navy may soon be comparable in strength to the Spanish or Italian fleets, but launching an aircraft carrier isn’t enough to make it competitive with the top powers, Cossa said.

“You need to be able to support it (an aircraft carrier) with missile boats and submarines, and all this looks like it is years away for China,” he said.

In an effort to gain experience in blue-water operations, the PLA Navy is ranging further from its home ports than many people realize, said Goldstein.

In recent years, it has made port calls in Fiji and New Zealand.

“China is building strategic relationships along the sea lanes from the Middle East to the South China Sea in ways that suggest defensive and offensive positioning to protect China’s energy interests, but also to serve broad security objectives,” a 2005 Department of Defense report said.

China’s Global Times newspaper recently reported that a Chinese company had taken over operation of the strategic Gwadar Port in Pakistan, at the door to the Strait of Hormuz and, according to some commentators, a potential naval base.

Goldstein said China’s presence in overseas ports has been almost entirely commercial so far, but he noted that if the PLA Navy wants to operate far from home, it will need places to refuel and repair its vessels.

“For years the Chinese have condemned countries having overseas bases,” he said. “We have seen ship visits but we haven’t seen efforts to build and sustain a base overseas. Someday that may come.”

In this photo released by China's Xinhua news agency, China's first aircraft carrier, the Liaoning, is anchored in the northern port in Qingdao, east China's Shandong Province, Wednesday, Feb. 27, 2013. The Liaoning has docked at its new permanent base where it will be responsible for operations in waters surrounding Japan and the Korean Peninsula, media reports said.AP